The Institute of Electrical and Electronics Engineers (IEEE) has adopted a set of standards for wireless local area networks (WLANs), known as 802.11, as well a set of standards for wireless metropolitan area networks (WMANs), known as 802.16. Wireless products satisfying the 802.11 and 802.16 standards are currently on the market, for example. The term, WiFi, is used herein to describe equipment satisfying the 802.11 standard. The term, WiMAX, short for worldwide interoperability for microwave access, is used herein to describe equipment satisfying the 802.16 standard.
In WiMAX orthogonal frequency division multiple access (OFDMA) downlink (DL) scheduling, the base station (BS) scheduler obtains channel feedback from a subscriber station (SS) to efficiently exploit multi-user diversity and enhance spectral efficiency. Specifically, the base station regularly receives channel quality indicator (CQI) information from the subscriber station. Thus, in a wireless neighborhood, the base station receives CQI information from the subscriber station, with which the base station updates a scheduling algorithm. The scheduling algorithm pertains to all subscribers in the wireless neighborhood, and determines transmission order, data rate, modulation type, and other characteristics of transmissions by the base station. Since the base station regularly receives CQI information from the various mobile stations in the wireless neighborhood, the scheduling algorithm is likewise regularly updated.
Among scheduling algorithms, frequency selective scheduling (FSS) can provide much more throughput compared with diversity scheduling. Frequency selective scheduling utilizes the multi-user diversity in each resource block (RB) and selects the best quality user in the resource block. The base station generates the resource block, for transmitting data to one or more subscriber stations. The base station may include one or more spatial streams.
While the frequency selective scheduling algorithm may be preferred over a diversity scheduling algorithm, the FSS algorithm requires the individual channel quality indicator (CQI) feedback from the subscriber stations in the wireless neighborhood. The CQI feedback may be individual CQI or continuous CQI. Thus, each subscriber station should feed the CQI of each resource block back to the base station, in order for the base station to successfully implement the FSS algorithm.
It turns out that it may be very challenging for each subscriber station in the wireless neighborhood to feed back the CQIs of each resource block, particularly where there are lots of resource blocks and lots of subscriber stations (users). With more resource blocks (given by M) and more subscriber stations (given by N), the base station is burdened with much more feedback overhead.
For example, if there are fifty subscriber stations and twenty-four resource blocks, assuming each CQI uses five bits, the total CQI overhead is expected to be 50×24×5=6000 bits. With this much overhead, full CQI feedback is not practical.
Some CQI compression algorithms have been proposed to reduce the overhead. For example, a best-M algorithm, an average best-M algorithm, and a bitmap algorithm have been proposed. The best-M algorithm and its variants, threshold-based CQI compression algorithms, require the subscriber station to feed the CQI of the best M resource blocks back to the base station.
Prior art designs have relied on different CQI formats. Thus, there is no agreed upon CQI format for transmission between the subscriber stations and the base station. Further, where compression algorithms are used, there is no standard representation of the compressed CQI before it is transported from the subscriber stations to the base station.
Thus, there is a continuing need for a full CQI feedback implementation that overcomes the shortcomings of the prior art.